Conventionally, for example, extension devices shown in FIG. 12 and FIG. 13 have been known as an extension device for a tripod leg apparatus (For example, refer to [online] Velbon Kabushiki Kaisha (retrieved on Feb. 28, 2007), Internet <URL: http://www.velbon.com/jp/catalog/classic/t100.html>.
An extension device shown in FIG. 12 and FIG. 13 is provided with a cylindrical upside tubular member 1 having an inner projection portion 1a for stopping fall-out, which protrudes inwardly at the lower end part thereof, a downside tubular member 2 having an outer projection portion 2a for stopping fall-out, that is, vertically movably inserted into the upside tubular member 1 along the axial direction thereof, protrudes outwardly at the upper end part, and is brought into contact with the fall-out stopping inner projection portion 1a of the upside tubular member 1 when protruded to the maximum with respect to the upside tubular member 1, and regulating means 3 such as locking means, which is secured at the upper end part of the downside tubular member 2 and regulates upward movement with respect to the upside tubular member 1.
And, the regulating means 3 has a pair of regulating members 5 such as dowels, which move outwardly in the diametrical direction by a pressing force of a pressing member 4 such as a compression spring, protrudes from the downside tubular member 2 from a hole portion 2b, and regulates upward movement of the downside tubular member 2 with respect to the upside tubular member 1 by being brought into contact with the lower end part of the upside tubular member 1.
Further, either one of the upside tubular member 1 or the downside tubular member 2 is made of brass, the thickness of which is 0.25 mm. Also, since the inner dimensions of parts other than the fall-out stopping inner projection portion 1a of the upside tubular member 1 are slightly greater than the outer dimensions of parts other than the fall-out stopping outer projection portion 2a of the downside tubular member 2, there is clearance between the upside tubular member 1 and the downside tubular member 2.